The present invention relates to a system for pointing and stabilizing an optical axis of an optical system. Specifically, a system is provided which permits correction of jitter in an optical system using a separate reference laser beam.
Optical imaging systems and lasing systems are available to provide a magnified image for viewing, and/or for projecting a precision laser for illuminating a distant target. These systems have an optical axis (bore sight) which is positionable in elevation and azimuth. The optical system is susceptible to vibrational forces which tend to impose a jitter on any optical signal being processed by the system. This substantially random motion of the optical system axis produces blurring of an image being magnified by the system. In the case of a lasing system, the motion imparted to the laser disturbs its pointing direction.
These vibrational influences can be minimized by stabilizing the platform supporting the optical system. The platform supporting the positionable optical system, such as the tripod of a camera or the robotic arm of a surgical laser, have stabilization systems which detect vibrational displacements of the platform, and attempt to apply a counterforce to the platform to oppose the vibrational displacements. However, there are certain performance limitations in this approach. For instance, high performance optical systems, having many optical elements, may have individual elements being disposed with different levels with respect to each other due to the vibrational forces resulting in vibration of the optical axis of the system.
Optical systems, therefore, have an additional requirement that not only is the platform supporting the system stabilized, but that the optical axis lying along the optical axis or optical line of sight be stable, so that images viewed from the system are stable, as well as maintaining the pointing position of any laser transmission system stable vis-à-vis the optical line of sight. The present invention is directed to maintaining the stability of the optical line of sight in a multi-element optical system.
In order to keep the optical line of sight stable, an inertial reference must be provided which identifies any apparent motion in the line of sight and which is corrected. In space applications, a star is commonly used as an optical inertial reference because there is no apparent motion relative to the Earth. A star, however, does not work as an inertial reference inside the Earth""s atmosphere because the atmosphere moves, and, therefore, anything viewed through the atmosphere tends to move.
Accordingly, in order to create the inertial reference and use it to maintain the pointing attitude stability of the optical line of sight, the present invention has been provided.
The present invention provides a system for pointing and stabilizing an optical line of sight in an optical system. The optical system includes a set of primary optics and relay optics which can be used to magnify an image received on one end thereof, or to transmit a laser to a precise location. A jitter rejection mirror is located in the path of the optical system, preferably near the point at which an image is viewed, or in which a laser originates in a laser pointing system. The jitter rejection mirror is positionable in response to an error signal generated by detecting a misalignment due to jitter between the optical system bore axis and a reference axis. The mirror is displaced in a direction to oppose any apparent change in the optical bore sight due to jitter.
In carrying out the invention in accordance with a preferred embodiment, changes in an inertially stable reference laser beam originating at the object side of the optical system is detected by an auto alignment sensor at the opposite end of the optical system. Jitter imposed on the optical system displaces the reference laser signal which is detected by the auto alignment sensor to generate a correction signal to position the jitter rejection mirror in a direction to cancel the jitter.